Panoramic images can, generally, be captured by employing systems that are classified as either dioptric systems, those that do not use reflective optics, or catadioptric systems that use both reflective and refractive optics. Dioptric systems include conventional cameras that employ wide-angle or fisheye lens based systems. Catadioptric systems generally include those employing conventional cameras with reflective optical elements in addition to refractive lens elements.
Conventional technologies can use a plurality of cameras to capture visual segments of a panoramic image and thereafter “stitch” the images together to form a more full panoramic image. These stitching systems thus cannot share a single viewpoint and the images will encounter parallax issues, which can be terms the single viewpoint (SVP) problem. The use of a single camera can be regarded as co-location of the viewpoints of multiple cameras which can overcome the parallax problem associated with multiple cameras.
The use of a wide-angle lens or fisheye lens can capture a panoramic image from a single camera. However, the use of a fisheye lens results in the capture of hemispherical panoramic images as would be expected when using a hemispherical field of view (FOV) lens. Alternatively, the use of a catadioptric system can overcome the SVP by capturing the panorama with a single camera aligned with a convex mirror. However, the use of a catadioptric system can be complicated by non-linear vertical resolution in the image resulting from the image being captured off of a highly curved reflective surface. Employing a conical reflective surface can improve vertical resolution uniformity at the cost of vertical field of view because the conical reflective surface acts as a radially symmetric planar mirror.
Cata-fisheye schemes have been employed to capture panoramic images. In a cata-fisheye scheme, the FOV of the fisheye lens and the FOV of the catadioptric element can overlap. This overlap region can employ shallow mirrors to capture high quality panoramic images. Further, wherein the overlapping region captures two viewpoints that are very close together, parallax is negligible and the SVP is effectively circumvented.
Generally, conventional panoramic imaging systems aim at obtaining visual information from a wide FOV. It is further typically desirable to have stereo views that enable 3D depth perception. These features can be important for a variety of real-world applications such as surveillance and autonomous navigation mission environments. A number of conventional panoramic stereo vision systems have been proposed in the literature. One category of conventional systems uses two or more omni-directional cameras, which are configured to produce either horizontal stereo image pairs or vertical stereo image pairs. Another category of conventional systems uses only one single camera combined with typically complex optics to achieve stereo vision. The various optical components of these types of conventional systems have been reported to include, for example, a hyperbolic double lobed mirror, multiple combined conic mirrors, four parabolic mirrors (with an orthographic camera), a concave lens with a convex mirror, a mirror pyramid, etc. The implementations with multiple omni-directional cameras bring various burdens, such as, data acquisition with multi-camera synchronization, lack of a compact system size, higher system costs due to the complex optical elements, etc.